The search/list view shows a SQL error - what can I do?

The search/list view shows the following SQL error:

An exception occurred while executing

'SELECT `geo_ort`, `geo_regionaler_zusatz`
FROM `tx_openimmo_domain_model_immobilie`
WHERE …
GROUP BY `geo_regionaler_zusatz`
ORDER BY `geo_regionaler_zusatz` ASC'

Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated
column 'tx_openimmo_domain_model_immobilie.geo_ort' which is not functionally
dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

Try to set the SQL mode:

sql_mode = ''

This can be done in config(system/additional.php as well:

<?php
$GLOBALS['TYPO3_CONF_VARS'] = array_replace_recursive(
    $GLOBALS['TYPO3_CONF_VARS'],
    [
        'DB' => [
            'Connections' => [
                'Default' => [
                    'dbname' => 'db',
                    'driver' => 'mysqli',
                    'host' => 'db',
                    'password' => 'db',
                    'port' => '3306',
                    'user' => 'db',
                    //'initCommands' => 'SET sql_mode = CONCAT(@@sql_mode, \',ONLY_FULL_GROUP_BY\')',
                    'initCommands' => 'SET sql_mode = (SELECT REPLACE(@@sql_mode, \'ONLY_FULL_GROUP_BY\', \'\'))',
                ],
            ],
        ],
    ]
);